TWENTYFIFTH EUROPEAN ROTORCRAFT FORUM
PaperNo: El
THE DEVELOPMENT OF AIRWORTHINESS REQUIREMENTS FOR CIVIL
NIGHT VISION GOGGLE (NVG) HELICOPTER OPERATIONS
BY
K.M.DODSON,N.TALBOT
FLIGHT DEPARTMENT
SAFETY REGULATION GROUP, CIVIL AVIATION AUTHORITY
GATWICK, UNITED KINGDOM
SEPTEMBER 14-16, 1999
ROME
ITALY
ASSOCIAZIONE INDUSTRIE PERL' AEROSP AZIO, I SISTEMI E LA DIFESA
ASSOCIAZIONE IT ALlAN A DI AERONAUTICA ED ASTRONAUTICA
(
THE DEVELOPMENT OF AillWORTHINESS REQUmEMENTS FOR CIVIL
NIGHT VISION GOGGLE (NVG) HELICOPTER OPERATIONS"
K.
M. Dodson &
N. Talbot
Flight Department, Civil Aviation Authority, UK
Abstract
Night VISIOn enhancing teclmology has been used by pilots in military aircraft operations for many years. Steady development and refinement of the teclmology, together with the availabili1y of associated equipment at reducing cost, has resulted in increasing interest in the use of Night Vision Goggles (NVGs) for specialist civilian aircraft operations. This paper briefly summarises the operating principles of NVGs and outlines the development, by the UK Civil Aviation Authori1y (CAA), of Airworthiness Requirements for civil NVG operations, following the findings of a proof of concept trial. The need for the requirements and the background to their development is explained, together with the main issues that the requirements need to address. An overview of the requirements is provided in Section 5 and the requirements are reproduced in full in Appendix l. Finally, an international perspective is provided by describing ongoing activi1y within the Joint Aviation Authorities (JAA) and the Federal Aviation Admirtistration (FAA) with the objective of producing hannortised requirements for civil NVG operations.
1. Introduction
There is increasing interest in using Night Vision Goggles (NVGs) for specialist civilian tasks; most notably for Police and Emergency Medical Services (EMS) operations. In January 1995, the UK CAA gave approval, on a trial basis, for one Police Constabulary Air Support Unit to undertake an evaluation of NVG operations using a BOlOS. The Devon & Cornwall Constabulary Air Support Unit believed the trial to be a great success, claiming safety and operational benefits for night operations. Consequently, other police forces are becoming increasingly interested and it was considered appropriate to develop formal requirements to support the use of civil helicopter NVG operations. Clearly, particular safeguards must be in place since there are potential hazards when the pilots view of the outside world is maintained solely by Night Vision Goggles. The military use of NVGs, over many years, has resulted in considerable experience of the benefits and hazards of their use. This experience was given due consideration by reviewing available military documents including, for example, any relevant Military Specifications (Mil Specs). The paper describes the background to the development of •he civil requirements and the significant airworthiness ,ssues that need to be addressed. The resulting requirements are presented in full in Appendix 1 to the paper.
The Devon & Cornwall Police Constabulary NVG trial carne to an end when the BO 105 was retired from service in 1998. The same Constabulary now operate a BK117 and the newly developed NVG requirements are currently being used to approve a full NVG modification to tllis aircraft.
Police and Emergency Medical Service NVG helicopter operations are being conducted in some other Joint Aviation Authori1y States and the FAA in the US have recently certificated civil NVG operations. Consequently, the JAA and FAA are discussing NVG requirements with the intention of producing harmonised airworthiness and operational rules. Information on tl1e progress of these discussions is also reported.
2. Principle of NVG Use and Potential Airworthiness Problems
In t11e electromagnetic spectrum, the human eye responds to wavelengths between 400 and 700 nanometres (nm) wllich we normally see as colours. However, as light levels reduce, the human eye is less able to distinguish colour and detail. On a dark night, colour perception is lost entirely and objects become shadowy, dim shapes. Night vision can be improved by increasing the amount of light reaching the eye, as with a torch for example, or by imaging teclmology by creating a visible phosphor-screen image from normally imperceptible radiation, as in a Night Vision Imaging System (NVIS). NVIS goggles consist of two image intensifier tubes and look much like binoculars mounted to a helmet. They operate by the amplification of light in the far red and near infra-red (IR) section of the electromagnetic spectrum (600 to 1000 nm). The two main 1ypes of intensifier tube in use are classified as Generation II, which uses a multialkali photocathode, and Generation III wllich uses the far more sensitive gallium arsenide photocathodes. Even at low light levels, a Gen III tube produces a very sharp image on the phosphor screen with little loss of resolution. The basic principle of the use of modern Night Vision Goggles is that the outside world is viewed through the goggles and the cockpit is viewed by looking "under" the goggles using the naked eye. The main way of meeting these differing requirements is to provide cockpit lighting that contains no infra-red. The use of the unaided eye to monitor the cockpit instruments requires them to be illuminated by acceptable amounts of visible light. If any illumination in the cockpit emits energy witllin tl1e response range of the IR-sensitive photocathode, it may degrade the performance of the goggles since they have a built in automatic gain device which reduces their sensitivi1y and resolution as the level of IR energy is " Paper presented at the 25"' European Rotorcraft Forum, Rome, Italy, September !999
increased. Therefore, to operate the goggles at maximum
efficiency, IR energy must as far as possible be eliminated from cockpit illumination systems. This non IR lighting has a characteristic blue/green colour and is achieved by the use of filters. Standard tungsten filament light bulbs produce approximately 95% of their energy in the infra-red wavelengths and hence will cause major interference with the performance of NVGs unless filtered. This includes warning lights, since a single unfiltered warning light illuminating at a critical phase of flight could cause loss of all external view, with the resulting obvious hazard.
It could be argued that loss of external view through the goggles would not be a problem as a reversion to conventional (non-NVG) flight could be carried out. Although this would be the case in some flight regimes, it is likely that NVGs will be used to manoeuvre the aircraft into situations that would be difficult to get out of without continued use of the goggles. Examples of this might be flight into a cloud topped valley or other operations close to obstacles. It would be potentially dangerous to provide the pilot with a piece of equipment that could be used to fly into difficult situations without also providing a reasonable expectation of adequate integrity and continued availability. For the purposes of drafting airworthiness requirements it is considered that a loss of external view for whatever reason in the critical flight condition should be classified as Hazardous, in accordance with the guidelines of JAR 29.1309 (Ref 1) and associated Advisory Material. This classification implies that the possibility exists for damage to the aircraft and for injury or loss of life, but falls short of the Catastrophic classification of JAR 29.1309, which implies total loss of the aircraft and occupants.
A classification of Hazardous seems appropriate for the critical flight phase, and drives provision of a defined degree of integrity for both goggles and cockpit compatibility through the mechanism of a System Safety Assessment.
3. BOlOS Civil NVIS Proof of Concept Trial A proof of concept trial was carried out by the Devon and Cornwall Constabulary Air Support Unit, with the objective of establishing the benefits, if any, to Police ·operations from the use of Night Vision Goggles. The aircraft used was the Air Support Unit's B0105, modified for NVG use and operated with GEC Ferranti NiteOp Gen III goggles. The initial phases of the trial involved the CAA, from both Airworthiness and Operational points of view. A CAA Test Pilot and a Flight Operations Inspector were involved in initial approval of the cockpit modifications and early operational use. The early, joint part of the trial was flown using two pilots.
Approval of the cockpit modifications was done without the benefit of formal airworthiness requirements, purely on an 'engineering judgement' basis, which was deemed adequate within the context of a limited trial closely controlled by the operational procedures applicable to
police operations. Nevertheless a subjectively good standard of cockpit compatibility was achieved but the process was lengthy and involved considerable discussion, highlighting the need for Airworthiness Requirements to simplifY both design and certification of such systems. Initial operating rules and crew training and qualification standards were established as a result of the initial joint f
CAA/Police part of the trial. These, combined with the airworthiness approval of the cockpit, aiiowed Devon and Cornwall Constabulary to continue the trial on an operational basis to assess fully the benefits of NVG use to their type of operation over a prolonged period of time without direct CAA involvement. The basic operational/airworthiness framework that was agreed had the foiiowing
features:-• Operations covered by Police Air Operators Manual, i.e. some aiieviation and special provisions given against normal Public Transport provisions.
• Permissible crew compliment of one pilot and one specially trained police observer with crew duties defined.
• Agreed standard of pilot/observer training.
• Minimum Transit Height for NVG use of 500 feet above ground level.
• No reduction in weather minima already established for normal night operations.
• No take off and landing permitted using NVGs. • Mandatory.Radio Altimeter, with low height warning
system.
• Flight Manual Supplement to detail limitations and procedures, e.g. NVG failure.
• Specified type of Night Vision Goggle.
The trial amassed a significant amount of NVG experience throughout the Devon and Cornwall geographic area. This area consisted of a mix of urban and rural areas, including very dark areas with little cultural lighting and also a considerable amount of coastline. Varied mixes of light conditions, both natural and cultural, and of ground texture were experienced within the context of a variety of police operational tasks. The types of task carried out included training, transit, location of 6 figure grid reference points, orbiting for search purposes, high (500 - 800ft) hovering and vehicle foiiowing. This experience allowed Devon and Cornwall Police to write a report assessing the benefits to police operations and to identifY any issues associated with NVG operations.
The report concluded that the use of NVGs provided a benefit to Devon and Cornwall Police operations. It is beyond the scope of this paper to present the benefits to police operations but the general experience gained relevant to airworthiness issues is described below. 3.1 Cockpit Lighting/Compatibilitv
The cockpit lighting was found to be generally satisfactory. Particular points identified were the importance of the additional low height warning light coupled with the radio altimeter, some difficulty with
differentiation of colour on gauges and the need to fit removable Fire Warning Light filters for NVG use. The latter was because it had not been possible to achieve adequate daylight readability with NVG filtered Fire Lights, resulting in the filters having to be removed for day use. A longer tenn solution of possibly combining filtered lights with audio fire warning was suggested, to avoid the configuration change.
3.2 Night Vision Goggle Equipment
The NVGs used had proven to be reliable. Attention was drawn to the need for separate battery power supply for each tube, to reduce the probability of total goggle failure. Battery management was highlighted as an important issue to avoid in-flight failures and a method for recording operating time for individual batteries was suggested.
The importance of correct helmet fitting and use of a counterbalance in order to provide a stable platform for the goggles were points highlighted, together with the importance of correct pre-flight goggle adjustment. 3.3 Crew Compliment
It was considered that the combination of pilot and specially trained police observer was appropriate and that Crew Resource Management had been an important part of training.
3.4 Hazards
Some potential hazards were identified with suggestions to minimise these.
Depth Perception was a problem in areas of poor texture, highlighting the importance of the radio altimeter and low height waruing system. Judging horizontal clearance was also difficult, e.g. when operating close to cliffs. A means around this was to use a horizontal reference such as the tide line on the beach but the problem was perceived as being similar to the difficulty with depth perception.
In the event of a partial, i.e. single tube, goggle failure, continued flight was considered acceptable although uncomfortable, but would be an adequate means to fly the aircraft to an area 'where conventional uight flight could be better carried out'.
To allow for continued flight in the event of goggle failure, it was emphasised that weather minima should not be reduced for NVG operations, although it was suggested that this might be possible in areas of high cultural lighting. The need for the pilot to continually make an assessment of the weather/visual cues that would be available for non-goggle flight was highlighted. Some concern was raised about the effect of goggle and counterbalance weight on the helmet in the event of an accident. The need to be able to remove the goggles quickly was identified and it was recommended that this
be done prior to an accident where possible. The problem
with this action however, ':vould be the consequent loss of
vision that could make an accident more likely, i.e. in the event of total power loss and engine off landing. In this case, even though there would be the chance of a heavy landing, or roll over, with a likelihood of additional injury caused by the weight of the goggles/counterbalance, continued use of the goggles to touchdown could siguificantly increase the probability of a safe landing being achieved. The report concluded that any additional risks associated with the additional weight seemed acceptable in the context of other perceived safety benefits, but it does highlight the aeromedical issues of NVGuse.
4. Background To The Development Of The Requirements
Some nations do not exercise control of police operations through their Civil Aviation Authority, using instead a
system of "State" control which has more in common with
military methods of control and approval. However, for nations who control such activities tluough their Civil Aviation Authority, including t11e UK, there is a need for appropriate Night Vision Goggle airworthiness and operational rules to be developed.
In the UK, the Civil Aviation Authority took the view tlmt the NVG proof of concept trial, using the BOlOS, should be considered complete when the aircraft was retired from service in 1998. Consequently, any clearance of an NVG modification to any other aircraft, including tl1e Devon & Cornwall Constabulary's BKl 17 to replace t11e BOlOS, should only be made against formally developed requirements. The trial had demonstrated a benefit to police operations and it was apparent that there was a continuing need for NVGs. Hence, it was considered appropriate to develop formal requirements to support t11e use of civil NVG operations.
Nevertheless, NVGs are highly specialised equipment and t11e CAA had no prior experience of their use by flight crew on civil aircraft. Although the CAA had some pilots with military NVG experience, the task of developing requirements was large and the likely timescale, due to other commitments, was inconsistent with the operational need.
However, the Police Constabulary Air Support Unit were able to enlist the support of the Home Office, the British Government Department responsible for the Police. The Home Office agreed to provide financial support to enable the CAA to contract an outside agency, with NVG experience, to provide advice on the development of the airworthiness requirements and thereby assist the Authority to produce appropriate requirements more quickly than would otherwise be possible.
Hence, the CAA prepared a project specification and invitation to tender and undertook to conduct a technical evaluation of the bids received, recommend who would be the most suitable contractor, manage the project and,
following its completion, review the project's findings and produce formal draft requirements.
The project specification outlined the objectives and scope of the project as follows:
• To deternline the airworthiness and operational factors influencing the safe, reliable and effective use ofNVGs and to evaluate their significance.
• To recommend ainvorthiness requirements and supporting guidance material for the approval of civil helicopter NVG operations.
Whilst the project would also identify the operational issues and risks of civil helicopter NVG operations, the primary aim was to develop airworthiness requirements, in the light of the operational issues identified.
The project was to include a search and review of all relevant literature, together with a review of the currently acquired experience of the use of NVGs to deternline t11e factors pertinent to the formulation of the requirements and any necessary guidance material. A review of all available nlilitary certification requirements and an assessment of their applicability for civil operations was also to be included. One example of such a document is tl1e US Military Specification "Lighting, Aircraft, Interior, Night Vision Imaging System (NVIS) Compatible" MIL-L-85762A (August 1988) (Ref 2) wllich addresses the issue of cockpit lighting compatibility.
Following the issue of an invitation to tender, five proposals were received and the contract was awarded to GKN Westland Helicopters Ltd. The study was duly completed and a number of findings and recommendations were made which covered the following
main issues:
• Lighting Compatibility • Low Height WarningSystem • Equipment Specification • Ergononlics
o Aeromedical Considerations o Flight Manual Supplement
• Operational Considerations
These issues are described in more detail in the following section.
5. Outline Of The Draft Requirements
In order to maintain an adequate level of safety, 1t 1s essential that during NVIS operations, continued compliance with the existing Airworthiness Requirements JAR 29 & 27 (Refs I & 3) is demonstrated. The findings of the study described above were used to formulate additional airworthiness requirements and advisory guidance material to support the approval of civil helicopter NVG operations and maintain the levels of safety achieved during normal aircraft operation.
The findings and recommendations from GKN Westland Helicopters Ltd were reviewed and refined by the CAA Flight Department to produce "Draft Ainvorthiness Requirements For Aircraft Equipped For Operations Using A Night Vision Imaging System (NVIS)". This material specifies additional requirements and limitations for aircraft equipped with NVIS. The requirements are intended to be generic and apply to any NVIS. To date, however, their application has been limited to Night Vision Goggles and it is accepted that they may need to be expanded for some alternative NVIS types.
In keeping with the existing airworthiness requirements, the NVIS requirements are broadly objective, to encompass changing technology, whilst supporting advisory material is also provided that is more detailed and identifies an acceptable means of compliance. The advisory material is referred to as ACJ (Advisory Circular Joint) material in line with the typical Joint Aviation Requirement (JAR) format.
The NVIS Airworthiness Requirements(AR) 1-13 are presented in full in Appendix I, but each rule is discussed briefly below. It should be borne in mind tlmt these are draft requirements subject to further consultation and the content could change in the event of justifiable conunentary on them and experience gained from their application.
ARl General
(a) This appendix specifies requirements and limitations equipped with an NVIS.
This rule is self-explanatory.
additional for aircraft
(b) The minimum standard of aircraft to which an NVIS will be applied shall be multi-engined and certificated for single or dual pilot IFR, non-NVIS night operations.
Because of the possibility of operations with very restricted visual cues, and taking into account as background information the generalities of the ADS33D type handling qualities criteria (Ref 4) developed in recent times, it was considered that an appropriate level of aircraft stability and control would be that required for IMC flight.
Multi-engined aircraft were considered appropriate to reduce the probability of a power off landing having to be carried out, and these aircraft being mostly Category A, have higher performance and systems integrity standards. (c) NVIS operations must not affect continued
compliance with the basic aircraft certification basis.
It was considered that there was no logical reason for compronlising the basic airworthiness standards that would apply for normal night flying, when considering NVIS approval. The appropriate JAR, FAR and British
Civil Airworthiness Requirements (BCAR), Section G (Ref 5) should continue to be met, e.g. colour differentiation of gauge markings.
(d) NVIS operations must be possible without exceptional pilot skill or alertness.
This rule is intended to avoid unusual complexity or difficulty in carrying out normal and emergency tasks whilst using NVIS.
AR2 Lighting Compatibility
(a) Continued compliance with Paragraph .1381 of the appropriate JAR must be demonstrated, during NVIS operations.
(b) Any light emitted from equipment, in either the cockpit or the cabin, during NVIS operations, must be compatible with the NVIS. (c) Any subsequent cockpit, cabin or external modification, including role equipment, involving a light emitting or reflecting device will require re-assessment.
These rules are intended to ensure that there can be no light sources within the cockpit that could cause a degradation of NVIS performance. This is primarily to avoid a hazardous situation due to ti1e illumination of unfiltered lights that could cause sudden loss of external
view.
The Advisory Material suggests, in some detail, a possible test methodology that can be used to demonstrate compliance with these rules.
AR3 (a)
Warning, Caution and Advisory Lights Continued compliance with Paragraph .1322 of the appropriate JAR must be demonstrated, during both NVIS and non-NVIS operations. This rule is intended to ensure that the pilot can still differentiate quickly and accurately between the Warning, Caution and Advisory lights displayed by the aircraft's warning system.
It is accepted that it may not be possible to use the original colours but nevertheless, reds and ambers must be identifiable as such, and clearly differentiated from each other and whatever advisory colour is used.
The overall attention getting capabilities of the warning system should not be degraded by the NVIS installation. Any degradation of the visual attention getting capabilities would need to be compensated by, for example, an audio warning system.
The guidelines of Military Specification MIL-L-85762A, Section 3.10.9.8 are suggested in the advisory material as a means of compliance.
AR4 (a)
Instrument Lights
Continued compliance of the NVIS compatible instrument lighting with Paragraph .1381 of the :1ppropriate JAR must be demonstrated durir•g non-NVIS operations.
It would be possible that measures taken to ensure NVIS compatibility could affect adversely normal usage of the cockpit. This rule is intended to ensure that normal daylight and non-NVIS night use of the cockpit is not compromised. This would include the transition from day into night flight when it can be difficult to achieve an acceptable solution, e.g. for Central Warning Panel brightness.
AR5 Dimming Levels
(a) The cockpit lighting must have a dimming range consistent with NVIS operations. The rule is self evident, but advice is given in the advisory material to help achieve an acceptable brightness level for day, non-NVIS night and NVIS operation. The advisory material assumes timt conventional lighting will be available for non-NVIS night flying, however it is conceivable that only one lighting system would be fitted, i.e. an NVIS compatible system which, by definition, is viewed by the naked eye and also has to comply with normal night lighting standards. The advisory material is not intended to prevent tile provision of an NVIS compatible lighting system only.
(b) Inadvertent selection between Day, Night and NVIS modes must be prevented.
The consequences of inadvertent selection of non filtered light could be severe. Again an assumption that there will be both conventional and NVIS compatible lighting in the cockpit is made, and equally, such provision is not mandatory. The advisory material suggests some means of switching which first requires a positive action, to minimise inadvertent selection.
AR6 Chromaticity and Radiance
(a) The chromaticity of the light sources in the cockpit and cabin must be sufficiently separated to ensure colour coding discrimination is maintained.
(b) The radiance of the light sources in the cockpit and cabin must be compatible with the selected NVIS.
These rules use the guidance of Sections 3.10.8 and Sections 3.10.9 and Appendix A of MIL-L-85762A to provide advisory chromaticity and radiance limits for cockpit and cabin light sources for a range of NVIS types. Using light sources which meet this standard is an acceptable means of compliance with the above requirement.
AR7 E>.1ernal Lighting
(a) External lighting systems must not unacceptably impair the performance of the NVIS.
This rule is self evident, but more relevant to civil operations than military. Civil aircraft are required to display the appropriate lights at all times whereas military aircraft will often operate lights-out for tactical reasons. The advisory material proposes a qualitative evaluation during flight trials.
(b) Continued compliance with Paragraphs .1383 to .1401 of the appropriate JAR must be demonstrated.
This rule requires that any external lights fitted, even though modified to minimise NVIS interference, must still meet the relevant existing requirements.
AR8 Low Height Warning System (a)
(b)
(c)
(d)
(e)
A radio altimeter display must be installed at every pilot's crew station from which NVIS operations are to be flown.
The fitted radio altimeter should have the following characteristics:
1) A display that is instantly visible and discernible during NVIS operations. 2) An expanded scale below 1000ft. 3) An integral fail/no track indicator. 4) An integral low height indicator light. If the cockpit has an EFIS or similar electronic displays, with an electronic radio altimeter presentation, then an additional visual low height indicator must he fitted to the instrument panel.
An unambiguous supplementary visual low height warning, that is discernible during head-up NVIS operations, must be fitted at every pilot's crew station from which NVIS operations are to be flown.
An unambiguous indication of radio altimeter fail, or no track within normal operating range, in addition to that provided by existing instrumentation, must be fitted at every pilot's crew station from which NVIS operations are to he flown.
The luminous area of the supplementary low height repeater light, additional low height indicator light (EFIS if applicable) and radio altimeter fail/no track light (if applicable) must be such that each is clearly visible under
(f)
all the conditions of flight in which the aircraft is cleared to fly.
The operation of any repeater lights must follow the logic of the installed radio altimeter, and must not flash.
(g) An unambiguous low height audio cue must be fitted, which is readily cancellable.
Night vision systems do not currently give adequate height perception in all conditions of light and ground texture. There is a high probability of encountering conditions that will result in a lack of height awareness by the pilot and
a
real probability of the aircraft flying into the ground, even when operations are not intended to be carried out at very low heights. It can be very easy to lose 500ft from a nominal operating height (of say 500ft), either due to a descent, or more likely, featureless rising ground. For this reason, it is considered essential that an adequate height reference system, with associated unambiguous warnings of low height and system failure, is provided to ensure safety of flight using NVIS.The importance attached to this is reflected by the detailed rules and associated advisory material. The effect of these rules is to require at each pilot's crew station an analogue radio altimeter with easily readable scale, repeater low height warning lights, radio altimeter no-track and fail warning lights and an unambiguous audio warning of low height.
AR9 Wire Strike Protection
(a) A wire strike protection system (WSPS) must be fitted to all helicopters cleared for NVIS assisted take-off and landing operations. This rule could be considered to be operational ratlter than airworthiness, and may be removed from these airworthiness rules. Currently, no request has been received for NVIS certification for take-off and landing. ARlO Equipment Specification
(a) The NVIS must be of a kind and design appropriate to its intended function.
This rule allows investigation of the suitability of any proposed NVIS. The advisory material makes recommendations as to NVIS characteristics, but rests heavily on MIL-L-85762A as being an established and accepted standard. Generation III, Type I or II Class B NVIS as defined in MIL-L-85762A, are proposed as the target standard equipment for civil applications.
It is arguable that a dedicated civil standard, such as a Technical Standard Order (TSO), should be created to define minimum NVIS standards, particularly in relation to reliability, as integrating military and civil requirements can be difficult and there is little control over any changes that might be made to military specifications.
' (b) The NVIS equipment and installation must comply with JAR 29.1309 Category A Requirements.
This rule is intended to ensure that the view outside the cockpit through the NVIS is provided with an adequate · ertainty of being maintained. The advisory material .tates that "the NVIS equipment and installation should be subjected to a system safety analysis in accordance with AMJ 25.1309. The loss of external view due to either goggle failure or interference by cockpit lighting is potentially Hazardous and appropriate consideration must be given to this functional failure in the system safety analysis carried out",
(c) Instructions for the Continued Airworthiness of the NVIS must be established.
It is important that the originally certificated NVIS standard is maintalned in service. Of particular importance is the management of battery life, if this is the chosen power source, Battery failure probably represents tile highest risk of goggle failure in flight and adequate means must be proposed to ensure that the probability of failure is low enough to comply witl1 ARlO(b).
ARll Ergonomics
(a) The NVIS configuration must not compromise the wearer's ability to perform normal duties. (b) Where the NVIS assembly constitutes an
additional fit to the protective helmet (i.e. it is not integrated with the protective helmet) a fast removal mechanism must be provided. (c) A fixed stowage receptacle, able to contain the
NVIS and batteries (where applicable), must be provided within reach of the crew while strapped in.
The ergonomics issues are fairly self evident but a requirement to cover these aspects helps to avoid unsuitable situations being presented for certification. A key issue here is t11e amount of available headroom to allow adequate head movement and the ability to hinge the goggles into the up position. The advisory material makes several recommendations on ergonomic issues to ensure easy operation when using NVIS.
The fast removal and goggle stowage requirements are intended to allow for the emergency landing case when the crew may wish to remove their goggles before landing, The stowage also prevents loose goggles becoming a hazard during normal (non-NVIS) operations.
AR12 Aeromedical Aspects
(a) The NVIS configuration mnst mimmisc the risk of impact injury to the wearer.
(b) The total mass of the head-borne NVIS assembly must not exceed 3.0 kg. If the total mass of the head-borne NVIS assembly exceeds 2.5 kg, human factors monitoring will be required.
(c) The centre of gravity (C of G) of the total head-borne assembly must be as close as possible to the natural centre of gravity of the wearer's head.
The aeromedical rules above are intended to minimise the probability of injury during accidents and also during normal NVIS use. The advisory material discusses the relative merits of frangible and non-frangible mounts for goggles but recognises that there is no clear answer on this subject The head-borne weight limit is based on current military advice, as is the rule and advisory material relating to centre of gravity,
AR13 Flight Manna! Supplement
(a) A specific NVIS supplement must be incorporated into the appropriate Aircraft Flight Manual.
It is considered that a Flight Manual Supplement must be provided to cover an NVIS modification and subsequent use. The Flight Manual Supplement should, as a minimum, address Limitations as specifically agreed between the Authority and the Operator such as minimum heights, types of operation, internal and external lighting configuration for NVIS operation, minimum equipment and minimum crew. Also included should be the procedures for emergencies and malfunctions, including NVIS failure, normal procedures and some descriptive material covering the NVIS and it's intended operation,
6. European/International Perspective
The NVIS requirements described above were prepared by the CAA in response to a specific and pressing need to generate requirements for the approval of aircraft and equipment for NVG operations in the UK As a result, the UK CAA acted unilaterally in the first instance to produce NVG requirements, However, Police and Emergency Medical Service NVG helicopter operations are being conducted in some other J AA States and tile FAA have also had a similar pressing need to approve NVG operations for EMS operators and have ordy recently certificated civil NVG operations.
Consequently, the JAA and FAA have now begun discussing the issue of NVG requirements in the Helicopter Joint Harmonisation Working Group with the intention of producing harmouised airworthiness rules. The FAA have produced airworthiness material largely based on advisory circular (AC) material, An initial comparison of this material with the UK CAA requirements has shown a large degree of commonality in
objective, but witb a different emphasis in the role of
advisory material versus requirements. It is our intention
tbat the requirements will ultimately form a Notice of Proposed Amendment (NPA) to JAR 27 & 29 but tbe precise metbod of promulgation has yet to be decided. A specific meeting to debate tbe issues and progress the task of producing harmoulsed NVG airworthiness material has been arranged with tbe FAA and is timed to coincide witb a US Night Vision Conference to be held in October 1999. Significantly, this conference includes a civil night vision workshop which reflects tbe increasing interest now being shown in tbe application of night vision equipment for civil flying operations. Completion of tbe harmonisation process, in due course, will result in agreed airworthiness material available for use by botb the J AA and FAA.
A parallel exercise is also ongoing to develop harmonised operational rules and it is intended tbat an appendix covering NVG operations will form part of JAR-OPS 3 (Ref6).
7. Conclusion
In response to increasing interest in using Night Vision Goggles for specialist civilian tasks, the UK CAA has developed "Draft Airwortbiness Requirements For Aircraft Equipped For Operations Using A Night Vision Imaging System (NVIS)". The requirements were produced following a proof of concept trial and a contracted study to determine all tbe factors influencing tbe safe, reliable and effective use of NVGs and tbeir significance for tbe approval of civil helicopter NVG operations. Consequently, tbe requirements address tbe significant airworthiness issues and provide a firm framework for tbe assessment of aircraft equipped for NVG operations. The requirements are currently being used to approve an NVG modification to a BKII7 for police operations. Police and Emergency Medical Service NVG helicopter operations are being conducted in some otl1er JAA States and recently also in tbe US. Consequently, tbe JAA and FAA have now begun discussing the issue of NVG requirements witb the intention of producing harmonised rules. The UK CAA draft airworthiness requirements will provide a significant input to Ibis process.
8. Acknowledgements
The authors wish to acknowledge tbe valuable assistance provided by tbe following individuals and companies: Capt P. Hannant, formerly Air Support Manager of tbe Devon & Cornwall Constabulary Air Support Unit; Capt P. Ashby, Chief Pilot, Devon & Cornwall Constabulary Air Support Unit; Capt M. Kenwortby, Police Aviation Adviser, Home Office; Mr C. Kitchen, General Manager, Applied Military Optics (a Division of Mann Avionics Ltd); Mr A. Scott, Avionic Systems, Marconi Electronic Systems; Mr B. Thomson, Oxley Avionics (a Division of Oxley Developments Company Ltd); and GKN Westland Helicopters Ltd.
9. References
l. Anon, Joint Aviation Requirements, JAR-29, Large Rotorcraft.
2. Anon, US Military Specification "Lighting, Aircraft, Interior, Night Vision Imaging System (NVIS) Compatible" MIL-L-85762A, August 1988.
3. Anon, Joint Aviation Requirements, JAR-27, Small Rotorcraft.
4. Anon, Aeronautical Design Standard ADS-33D, Handling Qualities Requirements for Military Rotorcraft, USAATC, July 1994.
5. Anon, British Civil Airworthiness Requirements, Section G Rotorcraft, Civil Aviation Autbority, August 1982.
6. Anon, Joint Aviation Requirements, JAR-OPS 3, Commercial Air Transportation (Helicopters), February 1999.
(
DRAFT
Appendix 1AIRWORTHINESS REQUIREMENTS FOR AIRCRAFT EQUIPPED FOR
OPERATIONS USING A NIGHT VISION IMAGING SYSTEM (NVIS)
1. Assumptions
1.1 Whilst it is acknowledged that both safety and operational benefits can be derived during NVIS operations, nevertheless in some circwnstances NVIS operations could carry an increased risk. These requirements have been written to minimise any potential risks. Employment of NVIS will enhance but not replace normal night VMC operations. In the event of a failure of the NVIS, a pilot must be able to revert to normal night VMC techniques. 1.2 "Lighting, Aircraft, Interior, Night Vision Imaging System (NVIS) Compatible" MIL-L-85762A (August 1988) guidelines will apply as a strategy to overall NVIS compatibility. This is a minimum requirement and if the applicant can demonstrate an improved capability this will be acceptable to the Authority.
l. 3 These generic requirements are intended to apply to any NVIS. To date, however, their application has been limited to Night Vision Goggles (NVG) and the requirements may need to be e>.:panded for some alt<,rnati·v(. . NVIS types.
l. 4 Pilots involved with NVIS operations qualified on type, and be current at non-NVIS,,,p.ight in accordance with current regulations. ,.::;f':lJc'r'··
3. Airworthiness Requirements ARl General
(a) This appendix specifies additional requirements and limitations for aircraft equipped with an NVIS. (b)
NVIS
st~:M·!if~ of:'air~ra:ft to which an and non-NVIS night
not affect continued air·cr:aft certification basis.
appr6ye~1,WJ~' ~\
flight ,, ••••i,']
~~~i~~-tiliT¥1:~:~~to~g~~c :~:~~~~n:d r~:~~i:~;e
18
,~~~
C::
''i
)!<' must be maintained. Applicable1.5 NVIS operations may be regimes.
EO
GEN (I, II or Ill)
G~i[i\l:i;ey6~
(1, 2 or 3) of Night Im,!girtg System JAR NVG NVIS Rad alt WSPS Joint Aviation Requirements Night Vision Goggles Night Vision Imaging System Radio AltimeterWire Strike Protection System
P'ii:ajil'aj:ll1s of the appropriate JAR include .771, .773, .1301, .1309, .1321, .1322 and .1381. FAA Advisory Circular AC 20-88 "Guidelines On The Marking Of Aircraft PowerPlant Instruments (Displays)" is also applicable.
(d) NVIS operations must be possible without exceptional pilot skill or alertness.
ACJ Material
Consideration should be given to the workload required to control the aircraft and it's systems during NVIS operations. Where possible, control functions associated with all other aircraft systems should be simplified to take account of NVIS operations.
AR2 Lighting Compatibility
(a) Continued compliance with Paragraph .1381 of the appropriate JAR must he demonstrated, during NVIS operations.
(b) Any light emitted from equipment, in either the cockpit or the cabin, during NVIS operations, must be compatible with the NVIS.
modification, including role equipment, involving a light emitting or reflecting device will require re-assessment. ACJ Material
The applicant should ensure compliance by applying the NVIS test methodology described below.
NVIS Installation Test Methodology
Stage I Prior to fitting to an aircraft, any NVIS compatible equipment should be viewed in a dark room facility will/ tl1e selected NVIS. During this assessment any unfiltered light will be detected and the effect of the lighting on the performance of the NVIS will be established. The testing should be carried out by suitably qualified engineers who have experience of NVIS compatible lighting and who are able to recognise the full range of effects due to unfiltered light sources.
Testing of permanently installed NVIS filtered equipment should include assessment of readability under simulated bright sunlight.
Appendix I
at the appropriate stage above. For all changes to tile cockpit configuration which include the addition of, or relocation of any device including non light emitting devices, such as straps, fire e":tinguishers, upholstery, clothing, carry-on equipment, etc., the operator should be aware that there is a potential impact on overall night vision compatibility, and therefore should carry out a cockpit assessment, as in stage 2 above.
Within the process described at stage 4 above, the applicant should demonstrate that cockpit transparency transmissivity does not significantly impair,the perfofl]lance of the selected
NVIS. · .. (; ( ,.;:·.•.
For aircraft
typ~~
.•
which:i~~l)!~i'()v[~lon
for light tight§Ifill~
unfiltered J.i!l~i'~~~i~?~..
~#~~r tl1e cockpit. Equally it will be necessaryio
[:(i~m\l)!#Jfi'~e.~t]i~\ light escaping from cabin windows hasiib
effedt'b1•1:Ji~cockpit NVIS. Such provision Stage 2 Following build of the aircraft, or modification, tl1eshC>l\IciiJ;ii'demonstrai¥!~:Jndet!.sfuges
4 and 5 of tl1e testing aircraft transparencies are blacked out to simulate a dark .,:niethq~()l0
gy:;aJ:>ove. ,:·;: :· ·night ambient lighting condition. The whole cockpit lighting i ·•·:· :)':i ·'1""· .•• ,,. •• • •
installation, and where applicable, cabin/equipment Jightirig: ,··
k: .·
V\l.ar~;~g;.,c;:;autiona\{d
Advisory Lightscan tl1en be assessed for: :•·•···
· .. '·-,':}'. )_:· \ _; .;· :·::::· :::,::>:: :::·j'_',::::::_::i;:' '//:-a) b) c) d) e) f) g)
readability of instruments, controls lighting balance of self illuminated
• ; ' panels and displays. :·••·· : ' · · · · attention
caution indicators and tl1e .
Stage 4 during flight trials the
installation in accordance with the
'Lighting System . . .. Exantination' methods specified in Sections · ·· of MIL-L-85762A, August 1988 (or its successor, as agreed by the Authority).
Stage 5 The tests detailed in stages 2 and 3 should be repeated during day and night flight in the aircraft's typical operating environment over the extremes of range of natural light levels caused by cloud cover, sun elevation, moon phase and elevation.
For any 'additional' cockpit, cabin or external modification involving a light emitting device, reassessment should begin
(a)c( i)CoJ~,W•.¥·~~:;,pq.inpliance with Pm·agraph .1322 of
.:\]l~i~gproprla~~··i~ must be demonstrated, during both . ~~<:and.~Qn~J\lyls operations.
.,. ·'"···:-'· .. -,_.,.,.,_._.._;T'''·
. i--.:y:-.//:·:'·'·:
i;''i\iJi~·%~~
be possible to obtain fully compatible warnings (red) and cautions (amber) captions without compromising sunlight readability. The lighting level defined in Section 3.10.9.8 of MIL-L -85762A, August 1988 (or its successor, as agreed by the Autl10rity) is designed to achieve a slight measure of incompatibility or flare in the NVIS, which provides a positive attention getting benefit, whilst not compromising tl1e view out of tl1e cockpit.The overall attention getting capabilities of the warning system should not be degraded by the NVIS installation. Any degradation of the visual attention getting capabilities would need to be compensated by, for example, an audio warning system.
AR4 Instrument Lights
(a) Continued compliance of the NVIS compatible instrument lighting with Paragraph .1381 of the appropriate JAR must be demonstrated during non-NVIS operations.
ACJ Material
The most common method of ensuring NVIS compatibility is to place filters over light sources to prevent emission of light from the portion of the spectrum which is visible to
(
NVIS. Where NVIS filters are used, it is preferable that they remain installed for day, night and NVIS flight, in order to simplify testing and subsequent operational management of the aircraft. This prevents problems associated witl1 stowages, loose articles, aircraft departing without filters fitted and filters falling off during flight. Other methods of achieving NVIS compatibility include the use of:
Light emitting diodes
Electro-luminescent panel floodlighting Incandescent floodlighting.
The lighting installation for non-NVIS operation should not be degraded by virtue ofNVIS compatibility.
AR5 Dimming Levels
(a) The cocl<pit lighting must have a dimming range consistent with NVIS operations.
ACJ Material
Appendix 1
disruption of cockpit vision at the high intensity. Instnunent and panel lighting is variable from extinction to full brightness.
NVIS: Warnings and cautions are presented at a fixed luminance of 15 footlamberts (fL) which maintains attention getting capabilities whilst not degrading the operation of the NVIS, in accordance with Section 3.10.9.8 of MIL-L-85762A, August 1988 (or its successor, as agreed by the Authority). Instrument and panel lighting is variable from extinction to full brightness and any non-NVIS filtered equipment lighting is extingui~hed.
Night and
AR6
'<:,,., .. ·::;;:;.,,
NVIS equipment presents an image to an observer by (a)":·• ·•:The light sources in the intensifYing light that is beyond the part of the spectrun1 ,fOCkpl('"c~li4> fabin separated to visible to the naked eye. The term used for emitted energy is' .. ensri~c;~p1.9~\'.cq~ing dis:d'iifuii!ia.tion is maintained.
Acit±~t~Al;' .. · .. ···} ...
radiance and is equivalent to luminance when referring
i6· ..
visible light emitted directly from a light source. The t~hh•·
for visible light reflected from a surface is
illuminanc~!anil.
·/' .. , .. , ·• "'•:::•·:.'',•:;:S!•!•
the equivalent for reflected energy visfBie .lf'Nyi'S conip~~)iFJY''is being achieved by filtering existing spectrum is irradiance. The term bri.ghltn~~.~~~§{i :~nerally i'Jl*~dsourc~~. lli~Ii filters should be selected to ensure the used to describe luminance and
!,·:d~sjitd\'c6ipil),·
separation. If NVIS compatibility is being irradiance cannot be termed···a9i\t"Wbil'i,b~.:iri~talling
intrinsically compatible light sources to the naked eye. It is true, '$~~·,:.~~;' :cfuomaticity co-ordinates need to have similarcompatible light,
corbifr·~~paration.
NVIS to ove:rlo:1d
user.
To
Day, Night and
view out of the the visible should and controls,
·~i .. ·'Lnu~• the goggles, with
defined as follows:
Day: Warnings and cautions are presented at full brightness. Instnunent and panel lighting are extinguished. Night: Warnings and cautions are presented at a brightness clearly discernible for night operation. If a dimming capability is provided, all annunciators, including master warning and caution, may be dimmable as long as the annunciation is clearly discernible for night operation at the lower lighting level. Undimmed annunciations have been found unacceptable for night operation due to
Sections 3.10.8 and Appendix A of MIL-L-85762A, August 1988 (or its successor, as agreed by the Authority) provides guidelines for the chromaticity of all cockpit and cabin light sources for a range of NVIS types. Using light sources which meet this standard is an acceptable means of compliance with the above requirement.
NVIS Class B standard cockpit lighting (as defined in MIL-L-85762A, August 1988 or its successor, as agreed by t11e Authority) is aimed at NVIS equipment with 665nm illters and will cause flaring of NVIS equipment filtered to a 645
nm cut off. However, experience has shown that this degree of NVIS flare has littJe effect on flight safety and therefore may not, as an isolated featnre, render
non
compliant an applicant's solution to NVIS compatibility based on 645nm cut off filters.(h) The radiance of the light sources in the cockpit and cabin must be compatible with the selected NVIS. ACJ Material
Sections 3.10.9 of MIL-L-85762A, August 1988 (or its successor, as agreed by the Authority) provide the radiance limits for cockpit and cabin light sources for a range of
NVIS types. Using light sources which meet this standard is an acceptable means of compliance with the above requirement.
AR7 External Lighting
(a) External lighting systems must not unacceptably impair the performance of the NVIS.
(b) Continued compliance with Paragraphs .1383 to .1401 of the appropriate JAR must be demonstrated. ACJ Material
If, during night flight assessment, as part of the NVIS installation test process, it is found !bat the performance of !be NVIS is impaired by !be external lights, it may be necessary to modifY the external lighting installation to obtain compatibility.
External lights which are non-NVIS compatible are increasingly likely to cause unacceptable flaring as height is reduced. The lighting of ground support vehicles should be assessed if appropriate.
The addition of external reflective surfaces, such as a white aerial on a skid, may also affect NVIS performance and may··
be subject to flight test. ·
ARS Low Height Warning System (a) A radio altimeter display every pilot's crew station from are to be flown.
~~;\~yduld normally be expected by giving bolb position and rate information.
(b) If the cockpit has an EFIS or similar electronic displays, with an electronic radio altimeter presentation, then an additional visual low height indicator must be fitted to the instrument panel.
ACJ Material
The visual low height annunciation provided by an EFIS display is urdikely to be as obvious as a discrete
Appendix l
incandescent lamp. The additional visual low height indicator is intended to provide an equivalent standard to that provided by an analogue altimeter with integral low height indicator light.
The additional visual low height indicator should be fitted as close to !be electronic radio altimeter presentation as possible, and in clear association.
The additional low height indicator is considered cautionary and should Jberefore be coloured an1ber accordingly. The
NVIS YELLOW colour as . A of
M!L-L-85762A, August 1988
Authority) is !be clo:sesl<a:t'P\\'~~*~\i@)\),lbis
be fitted on the edge of the coaming por:iti<)n :sltc,lild be such that !be pilot ·"''"5 ''" cue from the full range
·all phases of flight.
light is considered cautionary and amber accordingly. The NVIS defined in Appendix A of M!L-L-1988 (or its successor, as agreed by !be closest approximation to tlris which retains
compatibility.
(d) An unambiguous indication of radio altimeter
fail, or no track within normal operating range, in
addition to that provided by existing instrumentation, must be fitted at every pilot's crew station from which NVJS operations are to be flown.
ACJ Material
The warning(s) may be provided, depending on !be aircraft configuration, by visual and/or audio means.
The rad alt failfno track indicator is considered cautionary and lberefore any visual indications should be coloured amber accordingly. The NVIS YELLOW colour as defined in Appendix A of MJL-L-85762A, August 1988 (or its successor, as agreed by the Aulbority) is !be closest approximation to Ibis which retains
a
measure of NVIS compatibility.If !be rad alt failfno track indicator incorporates
a
light, !ben it should be co-located with the low height indicator on the instrument panel coarning in front of the pilot.Confusion with the low height repeater should be avoided. This could be achieved by providing dedicated audio cues.
(
(e) The luminous area of the supplementary low height repeater light, additional low height indicator light (EFIS if applicable) and radio altimeter fail/no track light (if applicable) must be such that each is clearly visible nuder all the conditions of flight in which the aircraft is cleared to fly.
ACJ Material
Since viewing distances in cockpits vary, the size of an object is defined in terms of angle subtended at the eye. The accepted acuity angle subtended at the eye for warning indicators, based on human factors research and used to define MlL STD 14 72D character sizes, is 6 milliradians. Allowing for the degraded vision offered by NVIS equipment, 10 milliradians is probably acceptable, but no data is available to prove it. Low height repeater lights fitted to current helicopters cleared for NVIS operations subtend up to 22 milliradians at the eye datum position. (f) The operation of any repeater lights must follow the logic of the installed radio altimeter, and must not flash.
Appendix I
the Authority) should be the target standard equipment for civil applications. Class B NVIS equipment allows red to be used in the cockpit.
It is recognised that some commonJy used NVIS do not comply with Class B requirements; however, experience of aircraft modifications has shown that a satisfactory level of compatibility can be achieved with such equipment. Where a class B NVIS is not available, compatibility with the cockpit installation shonJd be demonstrated as acceptable by following the NVIS Installation Test Methodology as described under section
---c,,,,,.,.
lighting to when the , the · Tllis may be occnJt '·The and the
~g~ed, w~hui~ar~:~~o::n~~;~a~~!~ht
audio cue mustbe,,,~J~~~~,r~~~"Ji}R
29.
ACJ Material helicopte~s{otifAR
2s.
~~;;rJ:~~;:;~
installation must·:J
A Requirements for aeroplanes).~r~:~~~:r ~~=u~c=~~:toc:C~~:i~e~:~~di~u~u~
0
s2ki~
.ACj~t~~~ji
· '
uot extinguish any low height visual
indicatio~~:
·' :,, . ,.':[~~ ~S ~qui~~e~t
and installation should be subjected to Audio cues should be designed tobe,L¢~\&i~~iit''~ith
theoverall aircraft audio cueing philos9p~Yii' , ,,,),{' · AR9 Wire Strilq>.J'rritection
Th~'J#9~~·.S~~W~·~form
ofwir~¥tP!i9M~h
system fitted to existing:,gFfi¢pRt~~:'i~,?nsists .. p~'~,;,i;ji:riingement of wire deflectors~
~i\~J.\#~.de~<;esfg~~
,(!lat
wires are deflected to acutting•'~~~c!ii:~~,~i·,ser~f~<r:~efore
they can damage critical aircrafts2#118h~~~;:
:
~Jg&neral
specification for a WSPS does not cn#~~~~i'9i¥:f: The system selected should be based on a consi~~ri1~6ii"'of the wire threats within the intended sphere of op~h\fiil~s.ARlO Equipment Specification
(a) The NVIS must be of a kind and design appropriate to its intended function.
ACJ Material
Generation III, Type I or II Class B NVIS as defined in
'a,s)iste~,i~~ety analysis in accordance with AMJ 25.1309.
' T))e:')q~~:>:q~'htemal view due to either goggle failure or
·
'*l~,t\~.i\i4c~by
cockpit lighting is potentially Hazardous andappropriate consideration must be given to this functional failure in the system safety analysis carried out.
(c) Instructions for the Continued Airworthiness of the NVIS must be established.
ACJ Material
Maintenance procedures should be specified and observed e.g. battery checks etc. The maintenance tasks should be included in the maintenance schedule of the aircraft as appropriate. General procedural instructions for equipment testing should be provided to prevent performance degradation which may become a source of hazard.
Appendix material to the appropriate JAR gives guidelines on the Continued Airworthiness information that should be determined.
ARll Ergonomics
(a) The NVIS configuration must not compromise the wearer's ability to perform normal duties.
ACJ Material
and demonstrate that they can be carried out safely, with emphasis on the considerations listed below:
a) The NVIS configuration should allow full head movement commensurate with all aspects of anticipated operation. If a goggle type NVIS incorporating a hinging mechanism is used, this should include the case of the NVIS hinged into the up position. In order to ensure free head movement, adequate clearance with all structure, with the pilot sat at the eye datum position should be demonstrated. The applicant should ensure that pilots are able to locate and operate from the eye datum position defined by the aircraft manufacturer such that they are able to consistently repeat the same seat adjustment position. If tlris is not possible, or if specific pilots choose to fly from an alternative seating position, then the applicant should ensure tl1at nrinimurn clearances are not compronrised for each pilot and that these pilots are able to consistently repeat the same chosen seat adjustment position.
b) The NVIS, should not impede the pilot's ability to scan the cockpit instruments.
c) The NVIS configuration should not prevent the pilot viewing the outside world with the un-aided eye.
Appendix 1
If the pilot elects to remove the NVIS in an emergency situation, then locating the NVIS in a stowage receptacle is a reliable means of ensuring that the NVIS does not become loose in the coc!<pit. Since under emergency conditions, time and convenience are of the essence, the stowage receptacle should be positioned for easy access. Good accessibility will also benefit general usage under normal conditions.
AR12 Aeromedical Aspects
(a) The NVIS eontfigllf.~Jt!on minimise the risk of impact injury to the
''
~f§~t~f,~. ~'~~~~~,~~::~~)~~g~~~~:.
1
~b.~etw~
een the eyes andd) The NVIS should not require continual adj!ustm<;~\· ,'' ~~ and will provide
in flight the eyes in the event of an
visor should be considered for the e) The NVIS should be easily removed and
'"''f'f"'
to the eyes or face is possible ;:;ingfl~~~re
the NVISassembl,~,, ~~~~l~t~s ,il,l~~~~!l;,~~~~~'i:~~~~?~,~~~~an~~d
if used, should be worn at all additional fit to the protective h~liij~~'J'(ii#i·h is iii(ti§~!iK':~r~:;unalJle to wear a protective visor because of integrated with the protective h¢iffi~t):•it<fast removal spectacles should be fitted with safety lenses. mechanism must be provided. . {.'•;·:\j}
. '•; ".; ~ ... '• ., -, . ' . . ;; :·:)::\'':,·
~~~~.~~.:~~i~li~~:~~;J!!·!~\le~ i~~iJ1
1
opf•ma·v··· i!J~if~:~~~t~~
Jl~'f:i#!<
ofin]~\illi
iheremoval''ffi~thod
mririM one hand
ACJ Material
When the NVIS is in the aircraft but is not being used for NVIS operations, then it should be restrained in the event of an accident. The restraining system should meet the general specification for crash protection specified for that aircraft. A dedicated stowage is recommended, since it is more likely to remain uncluttered by other items. The design of the stowage receptacle should be commensurate with the need to protect delicate optical eqnipment but should also enable the NVIS to be quickly stowed. It should be possible to open and close the stowage compartment with one hand, using a single action.
The applicant should ensure that helmet fittings are performed with the NVIS attached, in order to nrininrise NVIS movement relative to the pilot's eyes.
The relative safety merits of frangible and non-frangible NVIS mounts used on NVG types are difficult to deternrine. There are differing perspectives on the subject. Military users in the UK wear non-frangible types which have the benefit of being less likely to be accidentally knocked off, as well as reducing the likelihood of a loose object hazard in the coc!<pit following a hard landing. Frangible types are used in the US, and US studies reviewing historical accident data claim evidence for reduced risk of neck injury witl1 frangible mounts. The applicant is advised to consider these issues, particularly with respect to NVIS stowage if the pilot elects to remove tl1e NVIS.
(b) The total mass of the head-borne NVIS assembly must not exceed 3.0 kg. If the total mass of the head-borne NVIS assembly exceeds 2.5 kg, human factors monitoring will be required.
ACJ Material
Any additional weight over and above that of the helmet is undesirable because of the muscular and skeletal loads
imposed on the neck in maintaining control over the head. These loads can result in both short and long term medical problems. Total head-borne mass is linked with weight distribution on the head as covered under requirement AR12(c). The aeromedical impact of increased weight on the head in fixed wing applications particularly under "g" loads 's well known and is the basis for the target figure stated. c) The total head-borne mass is made up of the protective d) helmet, any additional electro optical equipment, the safety
visor and counterweight. e)
In exceptional circumstances, where total head-borne mass is permitted to exceed 2.5 kg, an annual human factors review will be required, particularly with respect to continued acceptance by the pilots and reported instances of medical related problems.
(c) The centre of gravity (C of G) of the total head-borne assembly must be as close as possible to the natural centre of gravity of the wearer's head.
ACJ Material
Centre of gravity of the total head-borne assembly is the primary factor associated with both long and short term neck strain injuries and is linked with total head-borne weight as·:: ·· covered under requirement AR12(b). In order to minimise.: strain on the neck, it is necessary to balance the head-bbrnci• mass about the natural C of G of the head. The mol11eni induced by the head-borne assembly
u~~:~:~~~!~'~el~~:~!
should not exceed 90 Newton.centimetresto the AO (Atlanta Occipital) Aviation Life Support Equipment and Neck Injury Amongst Night Rotary Wing Mishaps. US A ~m,;·.::o;';\'(
Laboratory · ··· 98-02, (a) ACJ Material mnst be Aircraft Flight
The Flight Manual Supplement should, as a minimum, address the following issues:
a) General.
b) Limitations: as specifically agreed between the Authority and the Operator.
1) Minimum heights. Appendix I 2) Weather minima. 3) Internal lighting. 4) External lighting. 5) Minimum equipment. 6) Minimum crew
Emergency and malfunction procedures. Normal procedures.
1)
